The present invention generally relates to flash memory devices, and more particularly, the present invention relates to address mapping techniques for flash memory devices.
In an effort to increase storage capacity, flash memory devices have been developed in which each flash cell is capable of storing two or more bits. These types of multi-bit memory devices are typically referred to as “multi-level cell” or “MLC” devices. In contrast, flash memory devices storing 1-bit data per memory cell are typically referred to a “single-level cell” or “SLC” devices. When compared to SLC flash memory devices, MLC flash memory devices offer the advantage of increased storage capacity, but suffer the disadvantage of increased write times. In addition, there have been relatively recent proposals relating to hybrid NAND flash memories which selectively utilize memory cells in either MLC or SLC modes.
In flash memories, each unit memory cell must be in an erased state prior to programming. In addition, erase functions are typically executed in units of erase blocks or erase zones containing large quantities of memory cells. These and other characteristics of flash memory necessitate the use of a “flash translation layer” (FTL) between the flash memory and the file system of the device. FTL generally functions to conceal the erase operations of the flash memory, and to emulate a storage device such as a disc drive or other mass-storage device. For example, during a write operation, the FTL functions to map physical addresses of the flash memory with logical addresses generated by the file system. In order to achieve a fast mapping operation, FTL uses an address mapping table typically composed of static random access memory (RAM).
One type of FTL includes log block mapping scheme. Generally, log block mapping utilizes log blocks as write buffers. This address mapping function of FTL allows a host to identify flash memory as a hard disk drive (HDD) or static RAM, and to access the flash memory in the same manner as an HDD or static RAM.
As suggested above, one important aspect of FTL functionality relates address mapping, and one example thereof is disclosed in U.S. Pat. No. 6,381,176 entitled ‘METHOD OF DRIVING REMAPPING IN FLASH MEMORY AND FLASH MEMORY ARCHITECTURE SUITABLE THEREFOR’, which is incorporated by reference.
Conventionally mapping schemes, however, are generally unsuitable or inefficient for an MLC flash memory device. In particular, writing speeds may not be desirable in the MLC flash memory device operable with conventional the log block mapping.